Compulsive hoarding is a poorly understood problem that includes excessive clutter, difficulty discarding and compulsive acquiring which are associated with considerable impairment and distress. The first phenomenological aim of this proposal (Study 1) is to study its (a) historical features and (b) relationship to other disorders, (c) to explore possible etiological features, and (d) to examine the validity of self-report measures of hoarding. The second aim (Studies 2 and 3) is to test predictions from an existing model of hoarding during laboratory studies of discarding and acquisition. Study 1 examines community and clinic samples with compulsive hoarding symptoms (n=120), clinic patients with OCD (n=120) and community controls without significant hoarding or psychiatric symptoms (n=120). Measures include standard diagnostic interviews of Axis I and II disorders, impulse control disorders, and self-report measures of hoarding symptoms, OCD, depression, and anxiety. Structured interviews for aspects of hoarding and insight, as well as pictorial, observer-rated and self-reported measures of clutter are completed in the homes of participants. Data on historical features of hoarding (e.g., age of onset, family history) will be examined in relation to hoarding symptoms and severity via logistic regression. Chi-square and logistic regression will be used to study the relationship of hoarding features to other Axis I and II condition. Exploratory analyses of possible explanatory/etiological factors in hoarding will be conducted using various statistical procedures. SEM analyses using multi-trait multi-method strategies will be used to validate self-reported hoarding symptoms against self- and observer-rated symptoms. Studies 2 and 3 will test hypothesized cognitive and affective features of hoarding through in vivo discarding and non-acquisition tasks conducted at home and in typical acquisition settings for hoarding (n=100) and community control participants (n=50) recruited from Study 1. During these tasks, participants' cognitive, emotional and behavioral responses during attempts to discard and resist acquisition will be monitored. These findings will contribute to improved understanding of emotional, behavioral and cognitive components of hoarding and their relationship to OCD and other disorders and provide a sound basis for developing treatment strategies to address this problem. [unreadable] [unreadable]